Stress Mitigation in Packaged Microchips

ABSTRACT

A package apparatus has a base coupled with a lid to form a leadframe package. The package has first and second exterior surfaces with respective first and second contact patterns. The first and second contact patterns are substantially electrically identical to permit the package to be either vertically or horizontally mounted to an underlying apparatus.

PRIORITY

This patent application claims priority from provisional U.S. patentapplication No. 60/832,742, filed Jul. 21, 2006, entitled, “PACKAGEHAVING A PLURALITY OF MOUNTING ORIENTATIONS,” and naming Timothy R.Spooner and Nelson Kuan as inventors, the disclosure of which isincorporated herein, in its entirety, by reference.

FIELD OF THE INVENTION

The invention generally relates to electronic device packaging and, moreparticularly, the invention relates to mounting orientations ofelectronic packages.

BACKGROUND OF THE INVENTION

Leadframe based packages commonly are formed to be surface mounted in ahorizontal orientation. Specifically, during use, the exterior packagesurface having the largest surface area (i.e., often referred to as the“bottom side” of the package) typically is surface mounted to a printedcircuit board or other similar interconnection apparatus. There aretimes, however, when this mounting orientation is not optimal. Forexample, as known by those skilled in the art, an accelerometer often isoriented along a specific axis. As such, it generally requires aspecific mounting orientation. The circuit board supporting theaccelerometer therefore must be mounted within the underlying device inthe correct orientation. Requiring that a circuit board be mounted in aspecific orientation can be cumbersome and inefficient.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the invention, a package apparatushas a base coupled with a lid to form a leadframe package. The packagehas first and second exterior surfaces with respective first and secondcontact patterns. In illustrative embodiments, the first exteriorsurface is in a plane that intersects the plane of the second exteriorsurface (e.g., the two planes are not parallel). The first and secondcontact patterns are substantially electrically identical to permit thepackage to be either vertically or horizontally mounted to an underlyingapparatus.

The base and lid illustratively form a premolded leadframe package witha chamber for receiving an integrated circuit. The package apparatusalso may have an integrated circuit (e.g., a MEMS device, such as anaccelerometer or a gyroscope) secured within the chamber. The integratedcircuit may be substantially identically electrically connected with thefirst contact pattern and the second contact pattern.

As premolded components, the lid and base include a moldable material.The first contact pattern may have a first plurality of contactssubstantially embedded within the moldable material of at least one ofthe lid and base. Of course, although embedded, the contacts are exposedfor mounting to an exterior apparatus. Accordingly, the moldablematerial does not completely encapsulate the contacts of thisembodiment. In a similar manner, the second contact pattern may have asecond plurality of contacts substantially embedded within the moldablematerial of at least one of the lid and base. In some embodiments, thefirst exterior surface is orthogonal to the second exterior surface.

In some embodiments, the base has a base leadframe that is in electricalcontact with a leadframe embedded by moldable material of the lid.Moreover, the base may have a plurality of walls that form a chamber forreceiving an integrated circuit.

In accordance with another embodiment of the invention, a method offorming a packaged integrated circuit forms at least one leadframe tohave a first plurality of contacts and a second plurality of contacts.Next, the method encapsulates a portion of the at least one leadframewithin a moldable material to form a base and a lid. Afterencapsulating, the method secures an integrated circuit to the base, andelectrically connects the integrated circuit with the a least oneleadframe. Specifically, the integrated circuit substantiallyidentically electrically connects with the first plurality of contactsand the second plurality of contacts. Finally, the method connects thebase to the lid to form a premolded package having first and secondorthogonal, exterior surfaces. After the package is formed, the firstplurality of contacts are on the first exterior surface, while thesecond plurality of contacts are on the second exterior surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing advantages of the invention will be appreciated more fullyfrom the following further description thereof with reference to theaccompanying drawings wherein:

FIG. 1 schematically shows a bottom perspective view of a packageconfigured in accordance with illustrative embodiments of the invention.

FIG. 2 schematically shows a bottom perspective view of another packageconfigured in accordance with illustrative embodiments of the invention.

FIG. 3 schematically shows a cross-sectional, partially exploded view ofthe package shown in FIG. 1 along line 3-3.

FIG. 4 schematically shows the package of FIG. 1 coupled with a printedcircuit board.

FIG. 5 shows a process of forming the packaged microchip shown in FIG. 1in accordance with illustrative embodiments of the invention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In illustrative embodiments of the invention, a premolded leadframepackage has at least two, non-parallel exterior sides with substantiallyelectrically identical contact patterns. Accordingly, such a package iscapable of being mounted in at least two different orientations (e.g.,on its side surface or on its bottom surface). Designers thus can orientthe package to the requirements of a particular application—they nolonger are limited to orienting the printed circuit board only. Detailsof various embodiments are discussed below.

FIG. 1 schematically shows a bottom, perspective view of a packagedelectronic device 10 (also referred to as a “packaged microchip 10”)configured in accordance with illustrative embodiments of the invention.Among other things, the packaged electronic device 10 can contain anintegrated circuit chip, such as an ASIC or a MEMS device (see FIG. 3,discussed below). For example, if a MEMS device, the packaged electronicdevice 10 can function as an inertial sensor, such as an accelerometeror gyroscope, or as a transducer, such as a microphone or microspeaker.

The packaged electronic device 10 shown in FIG. 1 has a base 12 that,together with a corresponding lid 14, forms a premolded leadframepackage 13 for containing circuitry, such as the above noted integratedcircuit chips and/or other circuitry. In a manner similar to many othertypes of packages, the leadframe package 13 of this embodiment has agenerally rectangular cross-sectional shape with six sides; namely, atop surface 22A, a bottom surface 22B and four side surfaces 20. The topand bottom surfaces 22A and 22B have larger surface areas than those ofthe side surfaces 20. As shown, some of the surfaces 20, 22A, and 22B ofthe embodiment shown are generally orthogonal to each of their adjacentsurfaces. Moreover, as discussed above and shown in FIG. 1, at least twogenerally nonparallel (e.g., orthogonal) surfaces 20, 22A, and 22B ofthe package 13 have separate but substantially electrically equivalentcontact patterns (generally identified by reference number “18”).

For example, one side surface 20 may have a first contact pattern 18,while the bottom surface 22B may have a second contact pattern 18. Inaccordance with illustrative embodiments of the invention, the firstcontact pattern 18 on the side surface 20 may be substantiallyelectrically equivalent to the second contact pattern 18 on the bottomsurface 22B. Among other ways, each contact (also identified byreference number “18”) of the first contact pattern 18 may have acorresponding, electrically equivalent contact 18 on the second contactpattern 18. Alternatively, one contact 18 (or more contacts 18) on thefirst contact pattern 18 may have multiple corresponding, electricallyequivalent contacts 18 on the second contact pattern 18. Accordingly, inthis example, the package 13 may mount to an underlying interconnectapparatus 24 (see FIG. 4, discussed below) either on its side surface20, or on its bottom surface 22B.

A set of one or more contacts 18 may be considered to be substantiallyelectrically identical or equivalent with another set of one or morecontacts 18 on another surface when either set may be used to make thesame electrical connection with the internal circuitry of the package13. For example, the internal chip may be a gyroscope having an outputfor forwarding an output signal identifying rotational movement. If thisgyroscope output is electrically connected to a first set of contacts 18on one side surface 20 of the package 13, and also to a second set ofcontacts 18 on the bottom surface 22B, then the first and second sets ofcontacts 18 each receive substantially identical electrical signals. Assuch, the first and second sets of contacts 18 are considered to besubstantially electrically identical. Accordingly, either the bottomsurface 22B or the side surface 20 may be mounted to an interconnectapparatus 24, thus providing flexibility in the mounting orientation ofthe package 13.

As noted above, electrical equivalence does not necessarily require aone-to-one relationship between the contacts 18 of two different sides.For example, one side of the package 13 may have a single contact 18 forforwarding a specific signal to, or receiving a specific signal from,internal package components. The package 13, however, may have two ormore contacts 18 on another side for providing the same electricalconnection (i.e., for forwarding or receiving the same specific signal).These two or more contacts 18 on the other side may be required toreceive the entire signal (e.g., each provides a portion of the signal),or both may receive the same signal.

Accordingly, the package 13 shown in FIG. 1 may be surface mounted to aprinted circuit board 24 or related apparatus on one of its sidesurfaces 20 (see FIG. 4, discussed below), on its bottom surface 22B, oron its top surface 22A (if it has contacts 18). The applicationtherefore can dictate the ultimate orientation. It should be noted thatthe number and positioning of contacts 18 can vary depending uponapplication.

Illustrative embodiments use conventional surface mounting techniques tosecure the package 13 to an underlying interconnect apparatus 24, suchas a printed circuit board 24. Of course, other embodiments may useother techniques for securing the package 13, such as with solder balls.

To improve stability, the contacts 18 illustratively are formed as farapart as possible on a given surface. For example, the two side surfaces20 may each have contacts 18 at or near its far corners. In someembodiments, however, the contacts 18 are not at the corners. If thecontacts 18 are embedded (discussed below) and flush with the moldingmaterial, the side or surface 20, 22A or 22B may provide much of thesupport.

It should be noted that discussion of adjacent sides or orthogonal sidesand the relationship of contact patterns 18 is illustrative of severalembodiments only. Such embodiments necessarily fall under the generalcharacterization of being two non-parallel sides. In other words, atleast one side having the noted contact pattern 18 is in a plane thatintersects the plane of the other side (having the electricallyidentical contact pattern 18). Moreover, as shown in FIG. 2, some ofthese non-parallel sides are not necessarily on adjacent sides (i.e.,FIG. 2 shows intermediate sides 22C that are between the primary sides20, 22A and 22B). Accordingly, discussion of adjacent sides, ororthogonal sides, is not intended to limit many other embodiments of theinvention.

FIG. 3 schematically shows a cross-sectional, partially exploded view ofthe packaged electronic device 10 shown in FIG. 1 along line 3-3. Thisview shows an internal chamber 32 formed by coupling the lid 14 to thebase 12, and the chip 16 mounted therein. Moreover, this view also showsa part of the interior leadframe(s) 26, its/their extension to thebottom and side surfaces 22B and 20, and its/their coupling to the chip16 via wirebonds 28.

Specifically, this figure shows the interior chamber 32 containingcircuitry, such as a chip 16 and/or analog circuitry. For simplicity,only the chip 16 is discussed. It nevertheless should be recognized thatdifferent circuitry (other than, or in addition to the chip 16) may bewithin the chamber 32.

The base 12 in this embodiment is a premolded, leadframe cavity-typebase, which has four walls 30 extending generally orthogonally from abottom, interior face to form a cavity. In a similar manner, the lid 14also effectively is a premolded, leadframe lid. In other words, the lid14 comprises a leadframe 26 encapsulated by molding material. Like thebase 12, the lid 14 also has exposed metal forming contacts 18 andelectrically connecting with the leadframe 26 of the base 12.Accordingly, this type of leadframe package 13 shown in FIG. 3 is formedfrom at least two leadframes 26. In alternative embodiments, however,the lid 14 does not have a leadframe.

The lid 14 secures to the top face of the walls 30 to form the interiorchamber 32. To ensure a proper physical connection, one or more details34 in the base 12 may mate with corresponding details 34 formed in thelid 14. For example, the details 34 of the base 12 may be upwardlyextending protrusions, while the details 34 of the lid 14 may becorresponding orifices. As noted above, physical connection of the lid14 and base 12 mechanically and electrically connects the leadframes 26of the lid 14 and the base 12. The lid 14 and base 12 thus form apremolded, leadframe-type package 13 (also referred to as a “premoldedpackage 13”).

As known by those in the art, a premolded package has a moldablematerial (e.g., polymeric material, such as plastic) molded directly toa leadframe. Such package type generally is formed before the chip 16 issecured to it. This package type thus typically is ready to accept thechip 16 without requiring any additional molding operations. In otherwords, a premolded, leadframe-type package is ready made to package theelectronic chip 16. This is in contrast to certain types of otherplastic packages, such as “overmolded” or “post-molded” packages, whichapply molten plastic to the chip 16 after it is coupled with leads ofits leadframe. It nevertheless is anticipated that some embodiments canapply to post-molded and other technologies. For example, among others,some embodiments may apply to ceramic packages or stacked laminatedpackages using leadframes, vias, or other conductive paths to makeappropriate connections.

FIG. 4 schematically shows the packaged microchip 10 mounted on one ofits side surfaces 20 to a printed circuit board 24. As shown, to improvemechanical stability, the package 13 is coupled to the printed circuitboard 24 at or near its corners. It should be noted, however, that someembodiments may mount the package 13 inwardly from its corners.

The contacts 18 may be any of a plurality of different types ofcontacts. Among other things, the embodiment shown in FIGS. 1-4 haspads, which are substantially embedded within the molding material ofthe package 13. It should be noted that the molding material does notcompletely encapsulate this type of contact 18—it must be partiallyexposed to electrically connect with an interconnect apparatus 24. Forexample, the contact 18 may be flush with the mold material.Alternatively, the contact 18 may be somewhat recessed within, orsomewhat protruding from, the mold material. In other embodiments,however, the contacts 18 may be pins extending from the package 13.

FIG. 5 shows a process of forming the packaged microchip 10 shown inFIG. 1 in accordance with illustrative embodiments of the invention.This process shows various primary steps of a much larger process.Accordingly, those in the art should understand that further steps maybe added, or some of the steps shown may be modified or omitteddepending upon the application.

The process begins at step 500, which processes a pair of leadframes 26.Specifically, the process stamps, etches, and/or bends, etc . . . afirst leadframe 26 for use as the base 12, and a second leadframe 26 foruse as the lid 14. Conventional techniques thus may form the leadframes26 so that they have the configuration shown in FIG. 3. Moreparticularly, as shown in FIG. 3, the leadframes 26 are formed to ensurethat the ultimately package 13 has contacts 18 on at least two adjacentsurfaces. In addition, the leadframes 26 also are formed to ensureproper electrical communication between the lid 14 and the base 12.

To improve fabrication efficiency, the process preferably uses batchprocessing techniques, which process two-dimensional arrays ofleadframes 26 that ultimately are diced. For simplicity, however, theprocess of FIG. 5 is discussed without application of batch processingtechniques.

The process continues to step 502, which encapsulates the leadframes 26in a molding material, such as a conventional plastic. Accordingly,after completing this step, the process has formed the primarycomponents of the leadframe package 13, which includes the lid 14 andbase 12 shown in the figures.

At this point, the process may secure the die 16 and circuitry withinthe base 12 (step 504). For example, the die 16 may be secured with aconventional adhesive or other apparatus to a die attach pad or similarsurface within the cavity of the base 12. Additional circuitry may beadded, such as an application-specific integrated circuit (i.e., anASIC) or a discrete circuit element (e.g., a capacitor).

After securing the die 16, the process electrically connects theelectrical interfaces of the die 16 with the leadframe 26 of the base 12(step 506). To that end, the process may connect the wirebonds 28 tospecified portions of the leadframe 26 in the base 12. For example, inthe simplified device 10 shown in FIG. 3, one wirebond 28 connects witha first lead to the left of the die 16 (from the perspective of thedrawing), while another wirebond 28 connects with a second lead to theright of the die 16. The lead to the left of the die 16 effectivelyforms two contacts 18; namely, one contact 18 on the bottom surface 22Band another, electrically equivalent/identical contact 18 on the sidesurface 20. The lead to the right of the die 16 connects to anothercontact 18 on the bottom surface 22B and an exposed metal lead at thetop of the base 12.

The process then concludes at step 508, which secures the lid 14 to thebase 12. Any conventional means may be used to secure the two together,such as by using an adhesive or an ultrasonic weld. For the embodimentshown in FIG. 3, the bottom portion of the lid leadframe 26 mechanicallycontacts the exposed metal at the top of the base 12. This mechanicalcontact electrically connects the lead positioned to the right of thedie 16 to a second contact 18 on the side surface 20 of the lid 14. Ofcourse, discussion of only two contacts 18 is for simplicity only.Actual applications often can have many more contacts 18.

The premolded package 13 shown in FIG. 3 thus has substantiallyelectrically identical contact patterns 18 on the bottom surface 22B andside surface 20. In other words, the package 13 may be horizontallymounted (i.e., mounted on its bottom surface 22B) or vertically mounted(i.e., mounted on its side surface 20, as shown in FIG. 4) to anunderlying interconnect apparatus 24. Accordingly, rather than requiringa chip manufacturer to produce one packaged microchip for verticalmounting, and a second, different packaged microchip with identicalfunctionality for horizontal mounting, various embodiments of thisinvention enable a single packaged microchip 10 to perform bothfunctions.

In addition to providing more flexibility for mounting the packagedmicrochip 10, using leadframe package technology as discussed shouldsignificantly reduce device cost when compared to many other packagingtechnologies, such as ceramic package technology. Accordingly,illustrative embodiments are intended to provide a lower cost, flexiblemounting solution in a number of applications.

Moreover, various embodiments permit additional uses. For example, sometest handling equipment and fixturing may be configured to testhorizontal parts, which are designed for horizontal mounting. Forvertical mounted (packaged) microchips, however, such a test device maynot suffice. Various embodiments, however, permit packaged microchipsthat are to be vertically mounted to be tested in a horizontalorientation.

Although the above discussion discloses various exemplary embodiments ofthe invention, it should be apparent that those skilled in the art canmake various modifications that will achieve some of the advantages ofthe invention without departing from the true scope of the invention.For example, the lid 14 can form a cavity rather than, or in addition tothe base 12. As another example, the package 13 can have adjacentsides/surfaces that are not substantially orthogonal (e.g., see FIG. 1),or packages having more or fewer than six sides. For example, thepackage 13 can have angled or curved surfaces between the top surface22A and side surface 20. Moreover, discussion of leadframes as providingthe conductive paths and contacts 18 is illustrative. For example,leadframes and other conductive members (e.g., vias) may provideappropriate connections and contacts 18. Accordingly, those in the artcan modify various aspects and still achieve the various advantages ofillustrative embodiments.

1. A package apparatus comprising: a base; and a lid coupled with thebase forming a leadframe package, the leadframe package forming a firstexterior surface and a second exterior surface, the first exteriorsurface forming a first contact pattern, the second exterior surfaceforming a second contact pattern, the first exterior surface being in aplane that intersects the plane of the second exterior surface, thefirst and second contact patterns being substantially electricallyidentical to permit the package to be either vertically or horizontallymounted to an underlying apparatus.
 2. The apparatus as defined by claim1 wherein the base and lid form a premolded leadframe package.
 3. Theapparatus as defined by claim 2 wherein the base and lid form a chamberfor receiving an integrated circuit.
 4. The apparatus as defined byclaim 3 further comprising an integrated circuit mounted within thechamber, the integrated circuit being substantially identicallyelectrically connected with the first contact pattern and the secondcontact pattern.
 5. The apparatus as defined by claim 1 wherein the lidand base comprise a moldable material, the first contact patterncomprising a first plurality of contacts substantially embedded withinthe moldable material of at least one of the lid and base, the secondcontact pattern comprising a second plurality of contacts substantiallyembedded within the moldable material of at least one of the lid andbase.
 6. The apparatus as defined by claim 1 wherein the lid comprises alid leadframe, the base comprising a base leadframe, the lid leadframebeing in electrical contact with the base leadframe.
 7. The apparatus asdefined by claim 1 wherein the first exterior surface is substantiallyorthogonal to the second exterior surface.
 8. The apparatus as definedby claim 1 wherein the first exterior surface is adjacent to the secondexterior surface.
 9. An apparatus comprising: a base; and a lid coupledwith the base to form a package having at least one leadframe, the baseand lid forming a plurality of exterior surfaces, the at least oneleadframe forming a first contact means on a first exterior surface, theat least one leadframe forming a second contact means on a secondexterior surface, the first exterior surface being orthogonal to thesecond exterior surface, the first contact means and second contactmeans being substantially electrically identical to permit the packageto be either vertically or horizontally mounted to an underlyingapparatus.
 10. The apparatus as defined by claim 9 wherein the firstcontact means comprises a plurality of contacts.
 11. The apparatus asdefined by claim 9 further comprising an electrical interconnectapparatus coupled with no more than one of the first contact means orthe second contact means.
 12. The apparatus as defined by claim 9wherein the package is a premolded leadframe package.
 13. The apparatusas defined by claim 12 wherein the base and lid form a chamber forreceiving an integrated circuit.
 14. The apparatus as defined by claim13 further comprising an integrated circuit mounted within the chamber.15. The apparatus as defined by claim 9 wherein the lid comprises aleadframe encapsulated in moldable material.
 16. A method of forming apackaged integrated circuit, the method comprising: forming at least oneleadframe to have a first plurality of contacts and a second pluralityof contacts; encapsulating a portion of the at least one leadframewithin a moldable material to form a base and a lid; securing anintegrated circuit to the base after encapsulating; electricallyconnecting the integrated circuit with the a least one leadframe, theintegrated circuit substantially identically electrically connectingwith the first plurality of contacts and the second plurality ofcontacts; and connecting the base to the lid to form a premolded packagehaving first and second orthogonal, exterior surfaces, the firstplurality of contacts being on the first exterior surface, the secondplurality of contacts being on the second exterior surface.
 17. Themethod as defined by claim 16 wherein encapsulating comprises:encapsulating a first leadframe with the moldable material to form thelid; and encapsulating a second leadframe with the moldable material toform the base.
 18. The method as defined by claim 17 wherein the firstleadframe is in electrical contact with the second leadframe afterconnecting the base to the lid.
 19. The method as defined by claim 16wherein the integrated circuit comprises a MEMS device.
 20. The methodas defined by claim 16 wherein encapsulating comprises embedding thefirst plurality of contacts within the moldable material.
 21. A packageapparatus comprising: a base; and a lid coupled with the base forming apackage, the package forming a first exterior surface and a secondexterior surface, the first exterior surface forming a first contactpattern, the second exterior surface forming a second contact pattern,the first exterior surface being in a plane that intersects the plane ofthe second exterior surface, the first and second contact patterns beingsubstantially electrically identical to permit the package to be eithervertically or horizontally mounted to an underlying apparatus.